In the 3GPP LTE system, in order to assist an evolved NodeB (eNodeB) to perform uplink channel measurement, the eNodeB configures the UEs located within the cell to send sounding reference signals (hereinafter referred to as the SRS) on certain time-frequency resources. Based on the received SRS measurement result, the eNodeB performs frequency-domain scheduling for the physical uplink shared channel (PUSCH) transmission of the UE, and determines a modulation and coding scheme used by the uplink traffic channel transmissions to improve the spectrum efficiency of the uplink.
In the LTE system, the channel bandwidth is divided into a plurality of resource blocks (RB), all uplink signals or channels are allocated by taking the resource block as the unit. In the frequency-domain, a width of one RB is 12 subcarriers, i.e. 180 kHz. The total number of resource blocks in the channel bandwidth is determined by the channel bandwidth, for example, in the LTE system, the 20 MHz bandwidth option comprises a total of 100 RBs, and the 10 MHz bandwidth option comprises a total of 50 RBs.
For the uplink channel sounding, when allocating SRS resources to the UEs, the eNodeB needs to ensure that the SRS transmission signals of the respective UEs are orthogonal to each other. For example, the eNodeB allocates different time resources (subframes), and/or different frequency resource (RB), and/or different code resources (cyclic shift) to respective UEs to divide available SRS resources within the cell, thus ensuring that the SRSs transmitted by the respective UEs do not interfere with each other. Furthermore, in order to ensure the single carrier characteristics (SC-FDMA) of uplink signals, the eNodeB always configures each UE to transmit the SRS in a plurality of consecutive RBs, i.e. the SRS transmission bandwidth always contains several consecutive RBs.
Aiming to the above-mentioned system requirements, the 3GPP LTE specification TS 36.211 Section 5.5.3.2 defined different SRS bandwidth configuration parameters (Table 5.5.3.2-1˜Table 5.5.3.2-4) for different channel bandwidths. For example, taking the 20 MHz bandwidth (the uplink comprises 100 RBs) as an example, see the following table:
SRSSRS-SRS-SRS-SRS-bandwidthbandwidthbandwidthbandwidthbandwidthconfigurationBSRS = 0BSRS = 1BSRS = 2BSRS = 3(CSRS)MSRS,0N0MSRS,1N1MSRS,2N2MSRS,3N30961482242461961323162442801402202453721243122434641322162445601203454164812421224374811638242
In the above table, the parameter “SRS bandwidth configuration” represents the total frequency-domain resources allocated by the eNodeB to the SRS transmission of all UEs within a cell, so that it is a cell-specific parameter; another parameter “SRS-Bandwidth” is UE-specific bandwidth allocated to the actual SRS transmission depending on the system requirements. For convenience, the SRS bandwidth configuration is represented by the variable CSRS, while the SRS-bandwidth is represented by the variable BSRS. In order to provide a flexible configuration, the eNodeB can respectively configure the parameters CSRS and BSRS based on the actual requirements. Taking the above table as an example, the cell allows eight kinds of SRS bandwidth configurations, wherein the minimum one has 48 RBs and the maximum one has 96 RBs; and for the UE-specific, it is allowed to have four different SRS-Bandwidth configurations, the minimum one can have four RBs, and the maximum one can occupy the entire SRS bandwidth configuration. Since in the LTE system, the minimum SRS bandwidth is 4RBs and it allows to transmit within the frequency-domain range of up to 96 RBs, thus there are 96/4=24 possible transmission starting positions in the frequency-domain. Accordingly, the eNodeB specifies an SRS frequency-domain position index parameter nRRC whose value range is integers in the [0, 23] for each UE, and according to this parameter, the UE can decide the frequency-domain position at which it sends the SRS.
From the point of view of frequency-domain resource allocation, on the one hand, in order to obtain better frequency-domain scheduling gain, the UE is desired to transmit the SRS within a relatively wide frequency range, i.e. the SRS transmission bandwidth needs to be set large, so that the eNodeB can obtain the uplink channel measurement result within the almost entire channel bandwidth; but on the other hand, considering that there might be a large number of UEs within a cell needing to transmit the SRS, while the total resources allocated to the SRS transmission in the uplink are limited, therefore, it is also desirable to limit the bandwidth for SRS transmission of each UE. To resolve this conflict, an SRS “Frequency hopping” mode was defined in the LTE specification. In the frequency hopping mode, although the bandwidth for each SRS transmission of the UE is relatively small, but by transmitting at different times and different frequency-domain positions, a wide bandwidth may be completely covered after one SRS frequency hopping period. Taking the frequency hopping pattern shown in FIG. 1 as an example, see the above table, assume that parameters CSRS=6, BSRS=3 and nRRC=0, the black box in the figure represents that the SRS is transmitted at the corresponding frequency-domain position, and the white box represents that the SRS is not transmitted. Assume that the eNodeB enables the SRS frequency hopping, each SRS transmission bandwidth is actually four RBs, after the SRS is transmitted at 48/4=12 different frequency-domain positions within one SRS frequency hopping period, it can cover the spectrum portion of the entire 48 RBs, then the frequency hopping pattern is continuously repeated in the next SRS frequency hopping period. Wherein, the starting RB offset sequence selected by the SRS transmission within one SRS frequency hopping period is called SRS “frequency hopping pattern”, in the example, the SRS frequency hopping pattern is {0, 6, 3, 9, 1, 7, 4, 10, 3, 8, 5, 11}. Although different UEs within a cell may have the same frequency hopping pattern, the conflicts of SRS transmission frequency-domain positions between the UEs can be avoided by taking the SRS frequency-domain position index nRRC as the “reference”, so that they do not interfere with each other.
A “tree” structure is adopted in the 3GPP specifications to assist to define the SRS frequency hopping pattern. The “tree” comprises up to four layers, respectively marked with b=0, 1, 2, 3, wherein b=0 corresponds to the top layer of the “tree”, that is, the root node. In the bth layer, the number of RBs contained in each node in frequency on the “tree” equals to mSRS,b, while Nb represents the number of branch nodes located in the bth layer and contained in the (b−1)th layer nodes. In the “tree” type structure, each node in the bth layer can be uniquely determined by a group of identifiers {n0, n1, . . . , nb} (0≦nb<Nb) in the 0th˜bth layers. Each node on the “Tree” represents the starting offset and bandwidth occupied by the SRS transmission in frequency-domain. See the example of a tree structure in FIG. 2, wherein, in each node, a digital ID nb is displayed.
If the eNodeB enables the SRS frequency hopping, on the one hand, the UE can determine the layer where it is located on the “tree” based on b=BSRS according to the SRS bandwidth configuration BSRS by configured by the eNodeB, and obtain that the actual bandwidth of each SRS transmission equals to mSRS,BSRS On the other hand, the UE can determine another layer where it is located on the “tree” based on b=bhop and according to the “SRS frequency hopping bandwidth” parameter bbop configured by the eNodeB, and obtain that the total bandwidth covered by the SRS frequency hopping equals to mSRS,bhop. Thus, based on the “tree” structure, it can easily define the SRS frequency hopping pattern: determine the offset and bandwidth of the corresponding SRS transmission in the frequency-domain according to the SRS transmission occasion counter nSRS, that is, determine a group of identifiers {n0, n1, . . . , nb}. In the 3GPP LTE specification TS 36.211 Section 5.5.3.2, the following equation is used to define nb (b=0, 1, . . . , BSRS):
      n    b    =      {                                                      ⌊                              4                ⁢                                  n                  RRC                                ⁢                                  /                                ⁢                                  m                                      SRS                    ,                    b                                                              ⌋                        ⁢            mod            ⁢                                                  ⁢                          N              b                                                            b            ≤                          b              hop                                                                                      {                                                                    F                    b                                    ⁡                                      (                                          n                      SRS                                        )                                                  +                                  ⌊                                      4                    ⁢                                          n                      RRC                                        ⁢                                          /                                        ⁢                                          m                                              SRS                        ,                        b                                                                              ⌋                                            }                        ⁢            mod            ⁢                                                  ⁢                          N              b                                                otherwise                    
The physics meaning of the above equation may be understood in two aspects, in one aspect, the reference position of SRS transmission is determined according to the SRS frequency-domain location index nRRC configured by the eNodeB: {nb=└4nRRC/mSRS,b┘ mod Nb|b=0, 1, . . . , BSRS}; in the other aspect, adding an SRS frequency hopping pattern frequency-domain offset Fb(nSRS) from the (bhop+1)th layer to the (BSRS)th layer on this basis to finally obtain the actual frequency-domain SRS transmission position. Please be noted that this equation unifies two cases of SRS frequency hopping disabled and enabled, and for the scenario that the SRS frequency hopping is disabled, the eNodeB only needs to configure bhop≧BSRS, then the lower branch in the following equation will not be used to calculate the frequency hopping pattern frequency-domain offset Fb(nSRS). When the SRS frequency hopping is disabled, it can directly calculate to obtain the SRS transmission frequency-domain position, and the SRS transmission frequency-domain offset with 4 RBs being the unit equals to └((4·nRRC)mod mSRS,0/mSRS,BSRS)┘·mSRS,BSRS/4. The example in FIG. 1 gives the association between the values of {n0, n1, . . . , nb} and the actual frequency hopping positions when the SRS frequency hopping is enabled. The frequency hopping pattern period equals to mSRS,bhop/mSRS,BSRS.
The SRS frequency hopping pattern determining principle comprises two points: (1) it is not repeated within one frequency hopping period, and fully covers the target SRS bandwidth configuration; (2) the frequency interval between two consecutive SRS transmission frequency-domain positions should be as large as possible. To meet the above-mentioned requirements, the 3GPP LTE specification TS 36.211 Section 5.5.3.2 also gives an equation to calculate the SRS frequency hopping pattern frequency-domain offset Fb(nSRS):
            F      b        ⁡          (              n        SRS            )        =      {                                                                                                                                  (                                                                        N                          b                                                ⁢                                                  /                                                ⁢                        2                                            )                                        ⁢                                          ⌊                                                                                                    n                            SRS                                                    ⁢                                                                                                          ⁢                          mod                          ⁢                                                                                                          ⁢                                                      Π                                                                                          b                                ′                                                            =                                                              b                                hop                                                                                      b                                                    ⁢                                                      N                                                          b                              ′                                                                                                                                                            Π                                                                                          b                                ′                                                            =                                                              b                                hop                                                                                                                    b                              -                              1                                                                                ⁢                                                      N                                                          b                              ′                                                                                                                          ⌋                                                        +                                                                                                      ⌊                                                                                    n                        SRS                                            ⁢                                                                                          ⁢                      mod                      ⁢                                                                                          ⁢                                              Π                                                                              b                            ′                                                    =                                                      b                            hop                                                                          b                                            ⁢                                              N                                                  b                          ′                                                                                                            2                      ⁢                                              Π                                                                              b                            ′                                                    =                                                      b                            hop                                                                                                    b                          -                          1                                                                    ⁢                                              N                                                  b                          ′                                                                                                      ⌋                                                                                          if            ⁢                                                  ⁢                          N              b                        ⁢                                                  ⁢            is            ⁢                                                  ⁢            even                                                                          ⌊                                                N                  b                                ⁢                                  /                                ⁢                2                            ⌋                        ⁢                          ⌊                                                n                  SRS                                ⁢                                  /                                ⁢                                  Π                                                            b                      ′                                        =                                          b                      hop                                                                            b                    -                    1                                                  ⁢                                  N                                      b                    ′                                                              ⌋                                                                          if              ⁢                                                          ⁢                              N                b                            ⁢                                                          ⁢              is              ⁢                                                          ⁢              odd                        ⁢                                                                    
According to the above equation, the UE can calculate the SRS frequency hopping pattern frequency-domain offset, so as to further determine the frequency-domain position of the SRS frequency hopping transmission. Similar solutions are also included in the U.S. patent application with the Patent Application No. of US20090238241 and the title of “FREQUENCY HOPPING PATTERN AND ARRANGEMENT FOR SOUNDING REFERENCE SIGNAL”.
It can be seen from the above equation that, even if the equation can unambiguously give the equation to calculate the SRS frequency hopping pattern frequency-domain offset and its form is relatively simple, the computational complexity of the UE is relatively high because the calculation involves multiplication (Πb′=bhopb Nb′), modulo (mod), rounding down (└•┘) operation and multiplication/division. In addition, the calculation of the reference position of the associated SRS transmission, i.e., determining the nb value according to the equation └4nRRC/mSRS,b┘ mod Nb, also relates to calculations such as division, rounding down, module and the like.
The UE uses the above-mentioned equation to on-line calculate the SRS frequency hopping pattern, which will bring no small complexity: if the soft way of processor is used to calculate, it will result in that the working frequency required by the UE processor is higher, increasing the power consumption; if the hardware circuit is used to calculate, it will increase the overhead of the hardware circuit, resulting in increased cost of the UE.
Additionally, although defining the SRS frequency hopping pattern based on the “tree” structure is relatively concise in form, the UE needs to respectively calculate the serial number nb of each layer on the “tree” structure according to the relevant SRS parameter configuration of the eNodeB at the time of implementation, and then obtains the SRS frequency hopping pattern through the subsequent processing, which also increases the complexity of the UE implementation.